What Are XMP Sidecar Files and How Lightroom Uses Them (June 2026)

XMP sidecar files are small external files that sit alongside your original RAW images and store all your edit instructions, ratings, and metadata separately from the image itself. If you have ever opened Lightroom Classic to find that months of editing work had vanished after a catalog crash, understanding XMP sidecar files could have saved you from that disaster entirely.

In this guide, I’ll explain exactly what XMP sidecar files are, how Lightroom uses them to record your adjustments without ever touching the original RAW file, and why enabling them might be one of the smartest decisions you make for your photo workflow in 2026.

We’ll also cover the key differences between storing your edits in the Lightroom catalog versus writing them to XMP files, the three biggest reasons to turn this feature on, and the situations where you might reasonably skip it.

What Are XMP Sidecar Files?

An XMP sidecar file is a small text-based file that stores metadata and editing information about a photo. XMP stands for Extensible Metadata Platform, an open standard originally created by Adobe and now maintained by the International Organization for Standardization (ISO).

Because the XMP format is XML-based and open, it is not owned by any single piece of software. Any application that knows how to read XMP can access the information stored inside, which is part of what makes it so useful for photographers working across multiple tools.

The word “sidecar” simply describes the relationship: this file travels alongside the main image file. If your RAW file is called IMG_0042.CR3, Lightroom creates a companion file called IMG_0042.xmp in the exact same folder. The two files stay together like a motorcycle and its sidecar.

RAW files from cameras like Canon, Nikon, Sony, and Fujifilm cannot store XMP data directly inside the file header in a way that all software can read. That limitation is why sidecar files exist. JPEG and TIFF files can embed XMP data inside the file itself, so Lightroom does not need to create a separate sidecar for those formats.

What Data Gets Stored in an XMP File

When Lightroom writes to an XMP sidecar file, it records a specific set of information. Here is what you will find inside:

• Develop adjustments – exposure, contrast, white balance, highlights, shadows, color grading, sharpening, noise reduction, and every slider you touched in the Develop module
• Metadata – title, caption, copyright, keywords, star ratings, color labels, and location data
• EXIF data – camera model, lens, aperture, shutter speed, ISO (originally embedded by the camera)
• IPTC metadata – creator information, image description, usage rights
• Crop and rotation settings
• GPS coordinates if assigned or already present

What does NOT go into an XMP file? Lightroom-specific data like virtual copies, smart collections, pick and reject flags, and slideshow or print settings stay inside the catalog only. Those features are exclusive to Lightroom’s own format and have no equivalent in the universal XMP standard.

How Lightroom Uses XMP Sidecar Files to Store Your Edits

To understand why XMP matters, you first need to understand how Lightroom approaches editing in general. Lightroom Classic uses what is called non-destructive editing. When you drag the exposure slider or apply a preset, Lightroom does not alter a single pixel in your original RAW file. Instead, it records a set of instructions describing what you want to do to that image.

By default, those instructions live exclusively inside the Lightroom catalog. The catalog is a proprietary database file (with a .lrcat extension) stored on your computer. Every image reference, every edit, every keyword is tracked inside it. The catalog is efficient and fast, but it is also a single point of failure.

When you enable XMP writing, Lightroom takes those same edit instructions and also writes them out to the companion .xmp sidecar file sitting next to your RAW file. The catalog still exists, and it still tracks everything. The XMP file adds a portable, external record of your work.

Lightroom can either write XMP files automatically every time you make a change, or you can trigger the write manually. I’ll cover exactly how to set that up in a moment.

What About ACR Sidecar Files (Lightroom v15.0 and Later)?

Starting with Lightroom Classic version 15.0 in late 2025, Adobe introduced a new file type called the ACR sidecar. These .acr files handle a specific scenario: AI-powered edits like Denoise, Super Resolution, and Distraction Removal generate so much data that writing all of it to an XMP file would make the XMP file enormous and slow down your catalog.

The ACR sidecar stores only the heavy AI edit data, while the standard XMP sidecar continues handling everything else. If you are using one of these AI features, you may notice both an .xmp and an .acr file appearing next to your RAW files. Both need to stay together with the original image for your workflow to remain intact.

Adobe designed this split specifically to prevent catalog bloating that was frustrating photographers who heavily relied on AI tools. The separation keeps things fast without sacrificing portability.

XMP Sidecar vs Lightroom Catalog: What’s the Difference?

This is one of the most common points of confusion in Lightroom discussions, and it comes up constantly in photography forums. The catalog and XMP sidecar files are not alternatives to each other — they work together. But they store different things, and that matters enormously when something goes wrong.

Here is a clear breakdown of what lives where:

Stored in the Lightroom Catalog only:

• Pick and reject flags
• Virtual copies of images
• Collections and smart collections
• Slideshow, print, and web module settings
• Face recognition data and people tags
• All edit history states (the full undo history)
• Folder structure references and image import records

Stored in XMP sidecar files (and readable by other software):

• All Develop module adjustments (current state, not the full history)
• Star ratings and color labels
• Keywords and keyword hierarchies
• Copyright and IPTC metadata
• Titles, captions, and location data
• Crop settings

The practical consequence is that if your catalog file gets corrupted or deleted, and you have XMP files for every image, you can reimport your photos and recover your develop settings, keywords, ratings, and metadata. You will lose virtual copies, collections, and flags — but the core editing work survives.

On the other hand, data stored only in the catalog is in a proprietary format that only Lightroom can read. A competitor application like Capture One or even Adobe’s own Camera Raw cannot access catalog data — but it can read your XMP files perfectly. This is the core argument for enabling XMP writing as part of your standard workflow.

3 Reasons to Enable XMP Sidecar Files in Lightroom

Photographers on forums like Reddit’s r/Lightroom and the Lightroom Queen community consistently come back to three core benefits when discussing why they keep XMP writing turned on. These are the arguments that have convinced me to treat it as a default setting.

1. A Real Backup of Your Edit Work

Your Lightroom catalog is not backed up every time you edit a photo. Even if you have catalog backup enabled, those backups happen on a schedule — daily, weekly, or when Lightroom quits. Between backups, a catalog crash means you lose everything you have done since the last backup ran.

XMP files update every time you make a change (when automatic writing is on). Your edits are written to disk alongside the actual image file, which you presumably already include in your regular file backup routine. This gives you a continuous, always-current record of your work that your backup software will pick up automatically.

2. Open Standard Compatibility With Other Applications

XMP is an industry-standard format. Adobe Camera Raw, Capture One, Mylio Photos, Photo Mechanic, digiKam, and many other applications can read XMP sidecar files. This means your ratings, keywords, and develop settings are not trapped inside a proprietary format.

If you ever want to switch from Lightroom Classic to another photo editor, your core editing work can travel with you. Without XMP, you are locked in — every adjustment exists only in a database format that no other software understands.

3. Multi-Computer and Multi-Catalog Workflows

Many photographers work across two computers — a desktop in the studio and a laptop for travel. Managing two separate Lightroom catalogs on separate machines is notoriously painful. XMP sidecar files offer a practical middle ground.

Because XMP files sit next to your images rather than inside a catalog, any edits you make on one machine write to the file on disk. When you move those files to the other computer, the XMP files come with them. Lightroom on the second machine can read the XMP files and display your current develop settings without any catalog syncing. Multi-computer users in photography communities cite this as one of the strongest practical arguments for XMP.

How to Enable Automatic XMP Writing in Lightroom Classic

Enabling automatic XMP writing in Lightroom Classic takes less than a minute. Here is exactly how to do it:

1. Open Lightroom Classic and go to the top menu bar.
2. Click Edit (on Windows) or Lightroom Classic (on Mac) and select Catalog Settings.
3. In the Catalog Settings window, click the Metadata tab.
4. Check the box next to “Automatically write changes into XMP”.
5. Click OK to confirm.

Once this is enabled, Lightroom will write an XMP sidecar file every time you make a develop adjustment, add a keyword, change a rating, or update any metadata. The process happens in the background and typically takes only a fraction of a second per file.

If you prefer not to enable automatic writing, you can trigger a manual save at any time. Select one or more images in the Grid view, then press Ctrl+S on Windows or Cmd+S on Mac. This forces Lightroom to write the current metadata and develop settings to XMP immediately. You will also find this option under the Metadata menu as Save Metadata to File.

A useful shortcut for bulk work: if you want to write XMP files for an entire folder of images you have already edited, select all images in that folder (Ctrl+A or Cmd+A in the Grid view) and then use Save Metadata to File to write XMP for every selected image at once.

When You Might NOT Want XMP Sidecar Files

Most photography guides stop after explaining the benefits of XMP writing, but there are real situations where turning it off — or at least reconsidering — makes sense. This is a gap that most competitors overlook.

Performance on older hardware: On a machine with a slow hard drive and a large catalog, having Lightroom constantly write XMP files in the background can cause brief stutters. If you are editing thousands of images in one session on older hardware, you may notice the lag. Switching to manual saves (Ctrl/Cmd+S at the end of a session) gives you control without constant disk writes.

Storage space: Each XMP file is tiny — typically between 5 KB and 20 KB per image. But if you have 200,000 RAW files in your library, that adds up to several gigabytes of XMP files. For photographers with tight storage constraints, this is worth considering, though for most people the storage cost is negligible compared to the size of modern RAW files.

When you use DNG format: Adobe’s DNG (Digital Negative) format is a different solution to the same problem. DNG files can store XMP metadata directly inside the file header, eliminating the need for a separate sidecar entirely. Photographers who convert their RAW files to DNG on import already have metadata portability built in, so an XMP sidecar adds no extra benefit.

Pure catalog-based workflows: If you work on a single computer, back up your catalog religiously, and never intend to use another application, the catalog alone may genuinely be enough. XMP adds the most value when you are worried about data loss or need portability.

Frequently Asked Questions

Final Thoughts on XMP Sidecar Files in Lightroom

Understanding what XMP sidecar files are and how Lightroom uses them to store your edits gives you real control over your photography workflow. The short version: they are small, portable, open-standard files that record your editing work outside the catalog, protecting you from data loss and giving your adjustments a life beyond Lightroom itself.

For most photographers, turning on “Automatically write changes into XMP” in Catalog Settings is a low-effort decision with meaningful long-term benefits. The only real reasons to skip it are if you are already working with DNG files, running on genuinely constrained hardware, or maintaining a single-computer workflow with disciplined catalog backups.

If you have ever lost editing work to a catalog problem — or if you have simply wondered why those mysterious .xmp files keep appearing next to your RAW images — now you know exactly what they are doing there. They are quietly keeping a copy of your work, just in case.